The present invention relates to the production of structures of composite material and more precisely to pieces of more or less complex shape, constituted by the superposition on a suitable support of layers of continuous pre-impregnated fibers particularly with a resin polymerizable by ionization and emplaced by deposition in contact.
The invention relates more particularly to a new technique for deposition in contact roving of pre-impregnated fibers. By roving is meant in the present description a group of agglomerated continuous fibers in the form of a ribbon or strip, a single roving or several rovings juxtaposed to form a layer being adapted to be deposited according to the invention.
The deposition in contact of such roving is well known and has the advantage of producing at reduced production cost pieces which can have complex shapes and comprising particularly concave portions, with the aid of deposition heads for pre-impregnated roving, for example with thermosetting resin.
However, all the heads for deposition in contact that are known, use the same technique of supplying the roving under a deposition roller consisting, to initiate a deposition sequence, impressing for example with the help of a pair of motor-driven pulleys, the free end of the layer of roving in the direction of the deposition roller so that they are pinched between this latter and the surface to be covered.
Thus, at the end of each deposition sequence, the layer must be sectioned, which takes place between the deposition roller and the supply pulleys and therefore requires, for the following deposition sequence, to xe2x80x9cpressxe2x80x9d said layer as explained above.
For the types and natures of pre-impregnated fibers usually used for such deposition, the xe2x80x9cpressingxe2x80x9d of the roving has no particular difficulties or problems, because the roving or layers have a sufficient rigidity.
However, difficulties arise when the roving or layers have insufficient rigidity. Their flexibility does not permit directing them suitably toward the point of anchoring on the support to be covered. The impossibility of driving being moreover worsened in the case in which the fibers are impregnated with a resin that is stickier than the usual resins. This is particularly the case generally with ionizable resins which are polymerized, after emplacement of the roving, by ionization in a polymerization unit.
The stickier nature of the resin moreover renders problematical the relaxing of the roving applied by the tractive pulleys in conventional deposition heads.
The present invention seeks precisely to solve these problems by providing a new technique for depositing in contact permitting the placement of roving which, for reasons of insufficient rigidity and/or too high sticky nature, cannot be handled by the conventional contact deposition heads for depositing in contact.
To this end, the invention has for its object a process for depositing in contact roving of pre-impregnated fibers particularly for the reduction of complex structures of composite material polymerized by ionization, in which at least one roving is, in the course of a deposition sequence, unrolled from a reel or the like, pressed and deposited on a surface to be covered with the help of a deposition roller or the like, then cut when the desired length of roving has been deposited, characterized in that it consists in maintaining substantially from one end to the other of each deposition sequence the roving in contact with said roller, the roving being unrolled substantially under only the traction of the deposition roller and maintained, at least at the beginning at the end of the path of deposition, pressed against said surface to be covered, and, at the end of the deposition sequence, spacing the deposition roller from said surface, then cutting the roving in its portion between the roller and the surface.
Preferably, and in the case particularly of roving having a highly sticky nature, between the roving spool and the deposition roller is constituted a zone for decreasing and regulating the tension of the roving generated a storage loop or reserve ensuring supply under low tension of the roving to said deposition roller.
The invention also has for its object a device for practicing the process described above, comprising a deposition head mounted on a digitally controlled machine comprising at least four axes of mobility and moveable relative to the surface to be covered and comprising a deposition roller, supply means for said roving to the deposition roller, means for breaking the roving and means for cutting the roving, characterized in that the deposition head comprises moreover means to press against the surface to be covered the portion of the deposited roving, at least at the two ends of the section of roving, in that said supply means for the roving are arranged such that the roving remains continuously in contact with the deposition roller or over a substantial portion of its peripheral surface and in that said cutting means are arranged to cut the roving downstream of the deposition roller in the direction of movement of the roving with respect to the roller.
Preferably, the deposition roller is mounted on a deposition head, movably in the direction of the surface to be covered.
According to one embodiment, said means for pressing the deposited roving against the surface to be covered are constituted by a secondary roller disposed upstream of the deposition roller, in the direction of movement of this latter relative to said surface to be covered, said secondary roller being retractably mounted.
Preferably, the secondary roller is moreover movably mounted relative to the deposition roller and controlled automatically such that, in the course of the deposition sequence, it will press the deposited roving onto the surface to be covered by rolling over at least the two end portions of the deposited section and, if desired, over all the length of said section as a function of the complexity of the pieces to be made.
The cutting means for the roving are constituted for example by a cutting member and an anvil, positioned on opposite sides of the roving in its portion extending between the deposition roller in the position spaced from the surface to be covered and a secondary roller in the pressing position of the second end of the deposited section of roving, the portion of the cutting means interposed between the roving and the surface to be covered being retractable.
The deposition head according to the invention permits depositing pre-impregnated roving whose rigidity and/or sticky character would prevent the use of conventional heads, so called roving pushers, described above. It of course also permits the deposition of pre-impregnated roving usable with such conventional heads.
The deposition head according to the invention is adaptable to any type of machine for emplacing pre-impregnated fibers for the production of composite pieces of all sizes and shapes, even the most complex, in particular those including concave surfaces and in particular for large pieces of which all or a portion of the fibers are emplaced by deposition in contact, these pieces being then subjected to polymerization by ionization.